Bonded fluff structures and process for producing same

ABSTRACT

Bonded fluff structures and a method for producing such bonded fluff structures in which a pulp sheet having a material suitable for producing fluff and a heat activatable fiber material is fiberized to produce a mixture of fluff and heat activatable fibers. The mixture is contacted with a hot air stream, heating the heat activatable fibers to an activation temperature. The resulting heated mixture is then deposited onto a forming structure, forming a bonded fluff/fiber composite matrix structure.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to bonded fluff structures suitable foruse as an absorbent material in personal care absorbent articlesincluding diapers, feminine pads, incontinence garments, and trainingpants which is required to handle relatively large amounts of dischargedbody fluids, especially repeated discharges of relatively large amountsof fluid in relatively short periods of time, and a method for producingthe same. More particularly, this invention relates to a fiberizationprocess for producing such bonded fluff structures. In addition, thisinvention relates to a method for producing three-dimensional anddensity gradient bonded fluff structures for use in personal careabsorbent articles.

[0003] 2. Description of Prior Art

[0004] Personal care absorbent products such as diapers, feminine pads,adult incontinence products, and training pants often include a layer ofabsorbent material and a backing layer or moisture barrier which isimpervious to fluid. The absorbent material includes a surface forcontacting the body of the user so that body fluids are absorbed intothe product and are contained by a moisture barrier.

[0005] Such absorbent materials are frequently formed as nonwovenfibrous webs, for example, fluff/binder/superabsorbent composite matrixstructures. In order to maintain proper integrity when adhered todistribution materials to allow undisrupted capillarity across theboundary between such absorbent material structures and the distributionmaterials, and through the absorbent structure, it is necessary to bondthe absorbent structure.

[0006] Conventionally, the body contacting surface of the absorbentmaterials in personal care absorbent articles is substantially flat anduniform. There are, however, several advantages to using a textured bodycontacting surface, such as a greater absorbent surface area andimproved anatomical fit. The method of this invention is suitable forforming contoured fibrous webs or pads which have an increased weight ofmaterial in selected regions. When forming pads of absorbent material,the regions having the greater weight of material generally have acorresponding greater degree of absorbency. Such contoured absorbentpads are particularly useful in articles that are subjected to a greaterfluid loading in certain “target” areas than in other areas. Forexample, in a baby diaper comprised of an absorbent bat or pad locatedbetween a liquid pervious inner layer and a liquid impervious outerlayer, the crotch and front areas of the diaper are more heavily wettedby the infant than the areas closer to the infant's waist or back. Asimilar situation may also arise in the case of wound dressings,incontinence garments, and feminine sanitary napkins.

[0007] Developments in nonwoven technology have made tremendous stridesover the past several years. Today, there exists a wide variety oftechnologies for forming nonwoven materials including meltblowing,spunbonding, melt spinning, solution spinning, carding, melt spraying,and wet/dry air laying. Many of these technologies are used individuallyto form single component materials. As an example, spunbonding is usedto form nonwoven materials which can be used in such articles asworkwear and personal care products including diapers. Meltblowing canbe used to generate fine pore structures adaptable for use as filtermedia or absorbents for oil and other liquids. Air laying can be used toform such products as fibrous wood pulp bats for use as absorbents indiapers and sanitary napkins. In contrast to such processes whichproduce single component materials, the method of this invention issuitable for producing multicomponent materials.

[0008] Diaper dermatitis is a skin condition resulting from theprolonged contact of wet occlusive diapers with the skin of the wearer.This prolonged contact can lead to excessive hydration of the outermostskin layer, thereby reducing the skin's ability to function as abarrier. As a result, there is an increase in the permeation ofirritants, susceptibility of the skin to physical damage, and invasionof the skin by microorganisms. Maintaining a normal skin hydration levelhelps the skin maintain its optimum barrier properties. Thus, it isimportant that personal care absorbent articles, to the extent possible,prevent excessive skin hydration while containing body exudates andproviding a soft, dry and comfortable feel to the wearer.

[0009] Current occlusive absorbent garments with flap liners hold bodyexudates against the skin of the wearer. Heat and moisture are preventedfrom escaping from the product due to the close fitting nature of theproduct designed to prevent leakage. This problem is most severe in theinsult region of personal care absorbent products. The flat linerprovides a high contact area with the skin which can act as a pathway toconduct back to the skin free liquid that is not locked up by theabsorbent core, especially when the product is under pressure at theinsult point, because the flat liner cannot provide a sufficient degreeof separation of the wearer from the free liquid. In addition, flatliners do not allow the insult region of the personal care absorbentproduct to communicate with the ambient air to allow humidity to bereduced in the insult region as well as away from the insult region.

[0010] There are a number of methods known to those skilled in the artfor addressing these problems including the use of breathable backsheets, waist vents, and leg vents. However, these methods suffer from avariety of deficiencies which render them less effective than desired.For example, waist and leg vents through the back sheet tend to eitherbe occluded against the skin or provide leakage pathways. Other knownmethods include the use of folded absorbent cores or layers under theliner to dry the liner. However, these methods require undesirableprocess options and economics. Three-dimensional absorbent fabrics, suchas those produced in accordance with the method of this invention, canbe used to address these issues.

SUMMARY OF THE INVENTION

[0011] Accordingly, it is one object of this invention to provide amethod for bonding of fiber structures which maintain proper integritywhen adhered to distribution materials so as to allow undisruptedcapillarity across the distribution/fibrous structure boundary.

[0012] It is another object of this invention to provide a method ofin-situ matrix bonding of fibrous structures using conventional productconversion machines without the addition of lengthy through air bondingovens.

[0013] It is another object of this invention to provide an absorbentmaterial for use in personal care absorbent articles, such as diapersand sanitary pads, having a density gradient.

[0014] It is yet another object of this invention to provide a bondedthree-dimensional fluff structure for use in personal care absorbentarticles.

[0015] These and other objects of this invention are achieved by amethod for producing bonded fluff structures by which a pulp sheetcomprising a material suitable for producing fluff and a heatactivatable fiber material is fiberized, producing a mixture of fluffand heat activatable fibers. The mixture of fluff and heat activatablefibers is then contacted with a hot air stream at a flow rate andtemperature sufficient to activate the heat activatable fibers withoutagglomeration of the mixture. The heated mixture is then deposited ontoa forming structure, such as a forming wire, resulting in formation of abonded fluff/fiber composite matrix structure.

[0016] In accordance with one embodiment of the method of thisinvention, the bonded fluff/fiber composite matrix structure is furtherprocessed in a manner which imparts a density gradient into thestructure, for example, by passing the bonded fluff/fiber compositematrix structure through an embosser.

[0017] In accordance with another embodiment of the method of thisinvention, the bonded fluff/fiber composite matrix structure is shapedto form a bonded three-dimensional fluff structure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] These and other objects and features of this invention will bebetter understood from the following detailed description taken inconjunction with the drawings wherein:

[0019]FIG. 1 is a schematic diagram of the hot air fiberization processused to produce the bonded fluff/fiber composite matrix structures inaccordance with one embodiment of this invention; and

[0020]FIG. 2 is a schematic diagram showing a bonded fluff/fibercomposite matrix structure comprising a density gradient in accordancewith one embodiment of this invention.

DEFINITIONS

[0021] As used herein, the term “nonwoven web” means a web that has astructure of individual fibers or threads which are interlaid, but notin an identifiable, repeating manner. Nonwoven webs have been, in thepast, formed by a variety of processes such as, for example,melt-blowing processes, spunbonding processes, and bonded carded webprocesses.

[0022] As used herein, the term “polymer” generally includes, but is notlimited to, homopolymers, copolymers, such as for example, block, graft,random and alternating copolymers, terpolymers, etc., and blends andmodifications thereof. Furthermore, unless otherwise specificallylimited, the term “polymer” includes all possible geometricalconfigurations of the material. These configurations include, but arenot limited to, isotactic, syndiotactic, and random symmetries.

[0023] As used herein, the term “bicomponent fibers” refers tomulticomponent fibers of various configurations including, but notlimited to, side-by-side, core and sheath, pie segments, and islands inthe sea configurations.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0024] The method for producing bonded fluff structures in accordancewith one embodiment of this invention comprises fiberizing a pulp sheetcomprising a material suitable for producing fluff and a heatactivatable fiber material resulting in formation of a mixture of fluffand heat activatable fibers. By the term “heat activatable” we mean afiber which tackifies upon heating. Suitable materials for producingfluff include, but are not limited to, cellulosic materials. Any heatactivatable polymeric fiber may be used to produce the bonded flufffibercomposite matrix structure of this invention. A particularly preferredheat activatable fiber is a polypropylene/polyethylene polymerbicomponent binder fiber. Such bicomponent binder fibers tackify at atemperature of less than about 550° F. (288° C.), more particularly lessthan about 350° F. (177° C.).

[0025] After formation of the mixture of fluff and heat activatablefibers, the mixture is contacted with a hot air stream having a flowrate and a temperature sufficient to activate the heat activatablefibers. The heated mixture is then deposited onto a forming structure,such as a forming wire, resulting in formation of the bonded fluff/fibercomposite matrix structure. The bonded fluff/fiber composite matrixstructure is then densified, for example, in a nip. In accordance withone preferred embodiment of the method of this invention, prior todensifying, the bonded fluff/fiber composite matrix structure is furthertreated with a hot air knife to maintain the temperature of thestructure at a desired level until it reaches the nip. A hot air knife,used for pre- or primary bonding a just produced microfiber to give itsufficient integrity, is a device which focuses a stream of heated airat a very high flow rate, generally from about 1000 to about 10000 feetper minute (fpm) (305 to 3050 meters per minute), or more particularlyfrom about 3000 to 5000 feet per minute (915 to 1525 m/min.) directed atthe nonwoven web immediately after its formation. The air temperature isusually in the range of the melting point of at least one of thepolymers used in the web, generally between about 200 and 550° F. (93and 290° C.) for the thermoplastic polymers commonly used inspunbonding. The control of air temperature, velocity, pressure, volumeand other factors helps avoid damage to the web while increasing itsintegrity. The hot air knife's focused stream of air is arranged anddirected by at least one slot of about ⅛ to 1 inches (3 to 25 mm) inwidth, particularly about ⅜ inch (9.4 mm), serving as the exit for theheated air towards the web, with the slot running in a substantiallycross-machine direction over substantially the entire width of the web.In other embodiments, there may be a plurality of slots arranged next toeach other or separated by a slight gap. The at least one slot isusually, though not essentially, continuous, and may be comprised of,for example, closely spaced holes. The hot air knife has a plenum todistribute and contain the heated air prior to its exiting the slot. Theplenum pressure of the hot air knife is usually between about 1.0 and12.0 inches of water (2 to 22 mmHg), and the hot air knife is positionedbetween about 0.25 and 10 inches and more preferably 0.75 to 3.0 inches(19 to 76 mm) above the forming wire.

[0026] The use of hot air during fiberization of fluff/bicomponentbinder fiber pulp sheets activates the bicomponent fibers, therebyincreasing the strength of the resulting composite matrix structure.

EXAMPLE

[0027] CR-54 pulp from U.S. Alliance Forest Products of Coosa Pines,Ala. and Danaklon ES-C polypropylene/polyethylene 2.0 dpf (denier perfiber), 6 mm bicomponent binder fibers from Danaklon a/s of Varde,Denmark were wet formed into pulp sheets. One of the sheets from thismatrix of materials, 90% by weight CR-54/10% by weight Danaklon binderfiber, was fiberized on a six-inch continuous energy transfer (CET)fiberizer to produce a bonded fluff/fiber composite matrix structure.Although the process of this invention is described in terms of a CETfiberizer, there is no intention to limit the type of fiberizer used toproduce the fluff/fiber mixture. Thus, for example, a hammermillfiberizer may be employed as opposed to a CET fiberizer. FIG. 1 is aschematic diagram of the hot air fiberization method of this inventionutilizing a continuous energy transfer fiberizer. In this method, 500cubic feet per minute of hot air was fed into a Chromalox 125 kilowattair heater which was subsequently divided into two air sources that feedthe fiberizer, tangential and stripper air. The temperatures andpressures at which this process was carried out are shown in Table 1:TABLE 1 Temperature Ranges Used During the Trial All Temperatures are indeg. F. Air Heater Temperature 609-633 deg. F. CET Outlet Temperature330-350 deg. F. Down Stream Air Temperature 500-522 deg. F. Air pressure3.2 psig. Forming Chamber Temperature 388-393 deg. F. Air KnifeTemperatures 310-355 deg. F.

[0028]FIG. 1 is a schematic diagram of the continuous energy transferfiberizer, in very general terms, used to form the bonded fluff/fibercomposite matrix structure of this invention. CET fiberizer 10 comprisesforming chamber 11 which contains the mixture of fluff and heatactivatable fibers used in the formation of the composite matrixstructure. Compressed air from a compressor (not shown) is heated in airheater 12 to a temperature in the range of about 350-700° F. 177-371 °C.). The heated air is introduced through CET outlet 15 at a temperatureof about 330-350° F. (165-177° C.) into forming chamber 11. The heatedmixture of fluff and heat activatable fibers in forming chamber 11 isdeposited onto collection or forming surface 14. As shown in FIG. 1,forming surface 14 is in the form of a continuous loop foraminous wirewhich travels in the direction of arrow 18. It will, however, beapparent to those skilled in the art that the collection/forming surface14 may take other forms, such as the form of a rotating drum. Formingsurface 14, as shown in FIG. 1, travels in the direction of arrow 18about a pair of rollers 16, 17, either one or both of which may bedriven. If desired, the speed of forming surface 14 can be variablydriven so that the line speed can be controlled in relation to thedeposition rates of the heated mixture of fluff and heat activatablefiber.

[0029] As previously stated, Table 1 shows the temperatures andpressures used during sample collection. The temperature of air heater12 was about 609-633° F.; the temperature at the CET outlet 15 was about330-350° F.; the temperature in forming chamber 11 was in the range ofabout 388-393° F. (198-201 ° C.); and the temperature of hot air knife13 was in the range of 310-355° F. (154-179° C.). Samples were collectedfrom the forming surface and pressure was placed on the materials byhand from a roller. Tensile strengths of the resulting material weremeasured, the results of which are shown in Table 2. TABLE 2 Heated-AirSample Control Tensile Strengths Tensile Strength 200 g/m² web 200 g/m²web (Grams) (Grams) 59.2 157.92 59.2 177.66 78.96 157.92 98.7 177.6674.01 ave. 167.79 ave.

[0030] As can be seen, tensile strengths for the bonded fluff/fibercomposite matrix structure produced in accordance with the method ofthis invention using hot air fiberization were significantly higher thanthe control material, thereby clearly establishing that the heatactivatable fibers were fused during fiberization. Indeed, tensilestrengths for the hot-air formed samples were more than two times higherthan tensile strengths of the samples formed without heated air. It is,thus, apparent that the method of this invention enables in-situ matrixbonding of fiber structures on conventional product converting machineswithout the addition of lengthy through air bonding ovens.

[0031] The bonded fluff/fiber composite matrix structure of thisinvention contains interfiber bonds throughout the structure. Thetemperature in the forming chamber 11 should be high enough to activate,that is tackify, the heat activatable fibers. The melted or heatactivated fibers form substantially uniform interfiber bonds throughoutthe matrix structure, particularly at the fiber crossover contactpoints, providing a nonwoven web that is soft and strong. Illustrativearticles that can be produced using the composite matrix structure ofthis invention include personal care absorbent products and componentsthereof, such as body-conforming sanitary napkin shells over anabsorbent core, shape-retaining diaper components, incontinent careproducts, and the like.

[0032] Suitable polymers for use in the composite matrix structure ofthis invention are selected from the group consisting of polyolefins,polyamides, polyesters, polycarbonates, polystyrenes, thermoplasticelastomers, fluoropolymers, vinyl polymers, and blends and copolymersthereof. Suitable polyolefins include, but are not limited to,polyethylene, polypropylene, polybutylene, and the like.

[0033] Absorbent personal care articles such as sanitary napkins,disposable diapers, incontinent-care pads and the like are widely used,and much effort has been made to improve the effectiveness andfunctionalities of these articles. Thick, flat, personal care articlesof the past that do not fit the shape of the human body and do notconform to the movements of the user have been largely replaced byresiliently conforming three-dimensional, body-shaped articles.

[0034] In accordance with one embodiment of the method of thisinvention, the bonded fluff/fiber composite matrix structure is shapedto form a bonded three-dimensional fluff structure. In particular, afterthe bonded fluff/fiber composite matrix structure exits forming chamber11, it can be deposited onto a three-dimensional surface as is taught,for example, by U.S. Pat. No. 4,761,258. Through vacuum control and amale or female assist device, the bonded fluff/fiber composite matrixstructure can be contoured to readily accept exudates. The resultingstructure is resilient and holds its shape. In accordance with a furtherembodiment, a film layer can be applied during this process to allowformation of a product with a cavity. The structures produced inaccordance with this embodiment are suitable for feminine care devicesand BM inserts.

[0035] In accordance with another embodiment of the method of thisinvention, the bonded fluff/fiber composite matrix structure is furtherprocessed in a manner which imparts a density gradient into the bondedfluff/fiber composite matrix structure. For example, after the fluff isdeposited onto forming surface or forming wire 14, it can then be passedthrough an embosser which imparts a density gradient into the structure.In particular, an insert can be a fluff/superabsorbent material(SAM)/fiber composite and be configured less dense in the target zoneand more dense as one moves away from this zone, thereby enabling fluidto be rapidly received and spread through the increasing dense regions.Because the structure is resilient, the intake area is ready forsubsequent insult due to the fluid draining from this structure, throughin-plane wicking and transfer and/or deposition into an underlyingstructure. Such a density gradient structure is shown is FIG. 2.

[0036] In accordance with one embodiment of the method of thisinvention, additional materials may be introduced into forming chamber11 so as to provide the resulting composite matrix structure withadditional desired features. For example, in accordance with oneembodiment, a superabsorbent material is added to the fluff/fibermixture in forming chamber 11. In accordance with another embodiment ofthis invention, an odor control material is added to the fluff/fibermixture. It will be apparent to those skilled in the art that otheradditions which impart a variety of characteristics to the end productmay also be incorporated into the fluff/fiber mixture.

[0037] While in the foregoing specification this invention has beendescribed in relation to certain preferred embodiments thereof, and manydetails have been set forth for purpose of illustration, it will beapparent to those skilled in the art that the invention is susceptibleto additional embodiments and that certain of the details describedherein can be varied considerably without departing from the basicprinciples of the invention.

We claim:
 1. A personal care absorbent article, comprising: a liquidpervious inner layer; a bonded fluff structure adjacent the inner layer,the bonded fluff structure comprising a fluff material and a heatactivated fiber; and a liquid impervious outer layer adjacent the bondedfluff structure; wherein the bonded fluff structure has a basis weightof about 200 grams/meter² or less and a tensile strength of at leastabout 100 grams.
 2. The absorbent article of claim 1, wherein the bondedfluff structure has a tensile strength of at least about 125 grams. 3.The absorbent article of claim 2, wherein the bonded fluff structure hasa tensile strength of at least about 150 grams.
 4. The absorbent articleof claim 1, wherein the heat activated fiber comprises a bicomponentbinder fiber.
 5. The absorbent article of claim 4, wherein thebicomponent binder fiber comprises polypropylene and polyethylenepolymers.
 6. The absorbent article of claim 1, wherein the bonded fluffstructure further comprises a density gradient.
 7. The absorbent articleof claim 1, wherein the bonded fluff structure has a three-dimensionalshape.
 8. The absorbent article of claim 1, wherein the bonded fluffstructure further comprises at least one superabsorbent material.
 9. Theabsorbent article of claim 1, wherein the bonded fluff structure isproduced by hot air fiberizing a fluff/heat activatable fiber pulp sheetresulting in formation of a fluff/fiber mixture and depositing saidfluff/fiber mixture onto a forming structure resulting in formation of afluff/fiber composite matrix.
 10. The absorbent article of claim 1comprising a diaper.
 11. The absorbent article of claim 1 comprising afeminine care article.
 12. A bonded fluff structure produced by hot airfiberizing a fluff/heat activatable fiber pulp sheet resulting information of a fluff/fiber mixture and depositing said flufffibermixture onto a forming structure resulting in formation of a fluff/fibercomposite matrix, wherein the bonded fluff structure has a basis weightof about 200 grams/meter² or less and a tensile strength of at leastabout 100 grams.
 13. A bonded fluff structure in accordance with claim12, wherein the bonded fluff structure has a tensile strength of atleast about 125 grams.
 14. A bonded fluff structure in accordance withclaim 13, wherein the bonded fluff structure has a tensile strength ofat least about 150 grams.
 15. A bonded fluff structure in accordancewith claim 12, wherein the heat activatable fiber comprises abicomponent binder fiber.
 16. A bonded fluff structure in accordancewith claim 17, wherein the bicomponent binder fiber comprisespolypropylene and polyethylene polymers.
 17. A bonded fluff structure inaccordance with claim 12, further comprising a density gradient.
 18. Abonded fluff structure in accordance with claim 12, further comprising athree-dimensional shape.
 19. A bonded fluff structure in accordance withclaim 12, further comprising at least one superabsorbent material.
 20. Abonded fluff structure in accordance with claim 12, further comprisingat least one odor control material.
 21. A disposable diaper comprising:a bonded fluff structure produced by hot air fiberizing a fluff/heatactivatable fiber pulp sheet resulting in formation of a fluff/fibermixture and depositing said fluff/fiber mixture onto a forming structureresulting in formation of a fluff/fiber composite matrix, wherein thebonded fluff structure has a basis weight of about 200 grams/meter² orless and a tensile strength of at least about 100 grams.
 22. A femininecare article comprising: a bonded fluff structure produced by hot airfiberizing a fluff/heat activatable fiber pulp sheet resulting information of a fluff/fiber mixture and depositing said fluff/fibermixture onto a forming structure resulting in formation of a fluff/fibercomposite matrix, wherein the bonded fluff structure has a basis weightof about 200 grams/meter² or less and a tensile strength of at leastabout 100 grams.
 23. A bonded fluff structure produced by hot airfiberizing a fluff/heat activatable fiber pulp sheet resulting information of a fluff/fiber mixture and depositing said fluff/fibermixture onto a forming structure resulting in formation of a fluff/fibercomposite matrix comprising bonded heat activated fibers.